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2004-20051
Half Hollow Hills High School Ms. FogliaAP Biology
2004-2005AP Biology
Chapter 24.
The Origin of Species
“Both in space and time, we seemto be brought somewhat near tothat great fact—that mystery ofmysteries—the first appearance ofnew beings on this Earth.”
— Darwin
2004-2005AP Biology
Essential Questions How and why do new species
originate?
2004-20052
Half Hollow Hills High School Ms. FogliaAP Biology
2004-2005AP Biology
What is a species? Biological species concept
defined by Ernst Mayr population whose members can interbreed &
produce viable, fertile offspring reproductively compatible
2004-2005AP Biology
Biological species concept
Eastern Meadowlark Western Meadowlark
Similar body & colorations, but are distinctbiological species because their songs &other behaviors are different enough toprevent interbreeding
2004-20053
Half Hollow Hills High School Ms. FogliaAP Biology
2004-2005AP Biology
Diversity & Taxonomy The Tree of Life
species are thesmallest unit atthe ends ofbranches
basic unit fororganizing &categorizingliving things
smallest unit bywhich wemeasure diversity
2004-2005AP Biology
Reproductive isolation Species concept hinges on reproductive
isolation biological barriers that impede members
from producing viable offspring before vs. after fertilization
pre-zygotic barriers (before the zygote) post-zygotic barriers (after the zygote)
2004-20054
Half Hollow Hills High School Ms. FogliaAP Biology
2004-2005AP Biology
Prezygotic barriers Impede mating or hinder fertilization if
mating occurs habitat isolation temporal isolation behavioral isolation mechanical isolation gametic isolation
2004-2005AP Biology
Habitat isolation Two species may occupy different
habitats within same area so mayencounter each other rarely
2 species of gartersnake, Thamnophis,occur in same area,but one lives in water& other is terrestrial
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Half Hollow Hills High School Ms. FogliaAP Biology
2004-2005AP Biology
Temporal isolation Species that breed during different
times of day, different seasons, ordifferent years cannot mix gametes
Eastern spottedskunk (L) & westernspotted skunk (R)overlap in range buteastern mates in latewinter & westernmates in late summer
2004-2005AP Biology
Behavioral isolation Courtship rituals that attract mates &
other unique behaviors to a speciesare effective reproductive barriers
Blue footed boobiesmate only after acourtship displayunique to their species
2004-20056
Half Hollow Hills High School Ms. FogliaAP Biology
2004-2005AP Biology
Gray-Crowned Cranesengaged in courtship
display, Kenya
What can you say?
2004-2005AP Biology
Mechanical isolation Morphological differences can prevent
successful mating
Even in closely relatedspecies of plants, theflowers often have distinctappearances that attractdifferent pollinators.These 2 species of monkeyflower differ greatly inshape & color, thereforecross-pollination does nothappen.
2004-20057
Half Hollow Hills High School Ms. FogliaAP Biology
2004-2005AP Biology
Mechanical isolation For many insects, male &
female sex organs ofclosely related species donot fit together, preventingsperm transfer lack of “fit” between sexual organs:
hard to imagine for us, but a big issue forinsects with different shaped genitals!
Damsel fly penises
2004-2005AP Biology
Gametic isolation Sperm of 1 species may not be able to
fertilize eggs of another species variety of mechanisms
chemical incompatibility sperm cannot survive in female reproductive tract
biochemical barrier so sperm cannot penetrate egg
Sea urchins release sperm& eggs into surroundingwaters where they fuse &form zygotes. Gametes ofdifferent species—red &purple —are unable to fuse.
2004-20058
Half Hollow Hills High School Ms. FogliaAP Biology
2004-2005AP Biology
Postzygotic barriers prevent hybrid zygote from developing
into a viable, fertile adult reduced hybrid viability reduced hybrid fertility hybrid breakdown
zebroid
2004-2005AP Biology
Reduced hybrid viability Genes of different parent species may
interact & impair the hybrid’sdevelopment
Species of salamandergenus, Ensatina, mayinterbreed, but mosthybrids do not completedevelopment & thosethat do are frail.
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Half Hollow Hills High School Ms. FogliaAP Biology
2004-2005AP Biology
Mule are vigorous,but sterile
Reduced hybrid fertility Even if hybrids are vigorous they may be
sterile chromosomes of parents may difier in number
or structure & meiosis in hybrids may fail toproduce normal gametes
Donkeys have 62chromosomes
Horses have 64chromosomes
Mule have 63 chromosomes!
2004-2005AP Biology
Habitat breakdown Hybrids may be fertile & viable in first
generation, but when they mateoffspring are feeble or sterile
Strains of cultivated rice hasaccumulated recessivealleles. Hybrids are vigorousbut plants in next generationare small & sterile.On path to separate species.
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Half Hollow Hills High School Ms. FogliaAP Biology
2004-2005AP Biology
Speciation Species are created by a series of
evolutionary processes populations become isolated
reproductively isolated geographically isolated
isolated populations evolveindependently
Isolation allopatric sympatric
2004-2005AP Biology
Allopatric speciation Allopatric = “other country”
geographic separation migration physical barrier
Harris’s antelopesquirrel inhabitsthe canyon’ssouth rim (L).Just a few milesaway on the northrim (R) lives theclosely relatedwhite–tailedantelope squirrel
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Half Hollow Hills High School Ms. FogliaAP Biology
2004-2005AP Biology
Sympatric speciation Sympatric = “same country”
isolation even thoughmembers of populationremain in contact
what causes this isolation? chromosomal changes
polyploidy mostly in plants oats, cotton, potatoes,
tobacco, wheat non-random mating
2004-2005AP Biology
Adaptive radiation Evolution of many diversely adapted
species when introduced to variousnew environmental challenges &opportunities
Drosophila
Geospiza
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Half Hollow Hills High School Ms. FogliaAP Biology
2004-2005AP Biology
Adaptive radiation in plants
Silversword allianceall descendedfrom a commonancestor 5mya
2004-2005AP Biology
Adaptive radiation Many ecological
niches open Evolution of many
diversely-adaptedspecies from acommon ancestorto fill niches Darwin’s finches mammals
2004-200513
Half Hollow Hills High School Ms. FogliaAP Biology
2004-2005AP Biology
Review Speciation is a process
populations become isolated geographic isolation
different environmentalconditions: food, predators, disease,habitat
different selection pressures genetic drift
reproductive isolation different selection pressures:
sexual selection
isolated populations evolveindependently
2004-2005AP Biology
Current debate Does speciation happen gradually or
rapidly perhaps in response toenvironmental change Gradualism
Charles Darwin Charles Lyell
Punctuated equilibrium Stephen Jay Gould Niles Eldredge
Niles EldredgeCurator
American Museum of Natural History
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Half Hollow Hills High School Ms. FogliaAP Biology
2004-2005AP Biology
Gradualism Gradual divergence
over long spans oftime assume that big
changes occur asthe accumulationof many small ones
2004-2005AP Biology
Punctuated Equilibrium Rate of speciation is
not constant species undergo
most change whenthey 1st bud fromparent population
as separate species,remain static forlong periods of time
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Half Hollow Hills High School Ms. FogliaAP Biology
2004-2005AP Biology
Stephen Jay Gould (1941-2002) Harvard paleontologist &
evolutionary biologist punctuated equilibrium prolific author
popularized evolutionary thought
2004-2005AP Biology
2004-200516
Half Hollow Hills High School Ms. FogliaAP Biology
2004-2005AP Biology
Evolution is not goal-orientedAn evolutionary trend does not mean that evolution isgoal oriented. The modern horse is the only survivingtwig of an evolutionarybush with manydivergent trends.
2004-2005AP Biology
Convergent evolution Flight evolved 3 separate times
evolving similar solutions to similar “problems”
2004-200517
Half Hollow Hills High School Ms. FogliaAP Biology
2004-2005AP Biology
Parallel Evolution parallel paths filling similar
niches thereforeexhibit similaradaptations but are not
closely related
2004-2005AP Biology
Coevolution Predator-prey relationships Parasite-host relationships Flowers & pollinators
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Half Hollow Hills High School Ms. FogliaAP Biology
2004-2005AP Biology
Darwin AwardsNamed in honor of Charles Darwin, thefather of evolution, the Darwin Awardscommemorate those who improve ourgene pool by removing themselves from it.The Darwin Awards salute the improvement ofthe human genome by honoring those whoaccidentally kill themselves in really stupidways.Of necessity, this honor is generallybestowed posthumously.
www.DarwinAwards.com